1. Field of the Invention
The present disclosure relates to an iontophoresis device for applying an electrical field to a drug dissociated into cations or anions in a solution to thereby percutaneously drive the ions (anions and cations) to a living body.
2. Description of the Related Art
Iontophoresis is a technique of applying an electric field to a drug dissociated into cations or anions in a solution to thereby allow the ions (anions and cations) to percutaneously transfer into a living body. This technique is considered a promising administration method in terms of little pain to the patient and high dosage controllability. Nowadays iontophoresis is applied to administration of various drugs.
However, ion mobility based on the application of an electric field tends to decrease in inverse proportion to molecular weight of an ion. In particular, a higher-molecular-weight ion is more difficult to permeate through a biological interface (e.g., skin or mucous membrane), especially, stratum corneum. Hence, it has been said that a drug containing macromolecules such as protein or peptide molecules is hardly delivered through iontophoresis.
JP 10-510175 A discloses an iontophoresis device as shown in FIG. 6, as a device capable of delivering such a drug containing macromolecules.
As shown in FIG. 6, the device is structured such that a biological interface contact member (transferring means) 215 is interposed between a drug holding part (reservoir layer) 214 and a biological interface (skin) 240, the contact member having a substrate (supporting layer) on which a plurality of needles 252 to be inserted into the biological interface 240 are formed, and an electrical potential applied from an electrode 211 allows drug ions in the drug holding part 214 to pass through holes (flow path) 253 formed inside the needles 252 and migrate into the biological interface 240.
As described in JP 10-510175 A, the needles 252 are formed into lengths sufficient for the needle to pass completely or halfway through the stratum corneum 241 with substantially or absolutely no damage on an underlying biological interface surface 242. More specifically, the length (LN) of the needle 252 is set to 1,000 μm (maximum) or shorter, particularly preferably, 1 μm to 500 μm. Hence, it is possible to eliminate pain in a patient at the time of delivering a drug. In addition, a porosity of the contact member 215 is set to 30% (maximum) or smaller. More specifically, the holes 253 or the needles 252 are formed in the contact member at the density of about 2,500 (holes or needles)/cm2. The holes 253 each have a length (LK) of 1 μm to 3,000 μm, particularly preferably, 10 μm to 1,000 μm, and the diameter of 0.03 μm to 300 μm, particularly preferably 0.1 μm to 100 μm. Hence, a drug purportedly can be delivered in sufficient amounts.
However, as a result of studies made by the inventors of the present invention, it was revealed that a delivery speed of a high-molecular-weight drug (drug containing macromolecules such as protein or peptide molecules) is far from sufficient even with the use of the device disclosed in JP 10-510175 A. In particular, the device faces a problem in that under such current or voltage conditions that cause no damage on the biological interface, it is impossible to deliver an effective amount of drug within a period acceptable as a drug delivery period.